By Brazil Stock Guide — Brazil’s final pre-election polls were much closer to Luiz Inácio Lula da Silva’s first-round result than to Flávio Bolsonaro’s. The PL candidate finished with 47.03% of valid votes, versus 45.16% for Lula, a gap of 1.87 percentage points.
An analysis by BTG Pactual comparing the final surveys from 10 pollsters with the election result shows that, on a simple average basis, the polls underestimated Lula by just 0.28 percentage point, but underestimated Flávio Bolsonaro by 4.33 points. The pattern matters more than the average: all 10 polls put Bolsonaro below his eventual vote share, while the errors for Lula were split between overestimates and underestimates.
The gap remains significant even after accounting for each poll’s stated margin of error. For Lula, six of the 10 surveys were within their respective margins: Gerp, Quaest, PoderData, Datafolha, Real Time Big Data and Nexus.
AtlasIntel, Futura, CNT/MDA and Meio/Ideia were outside their stated margins for Lula.
For Flávio Bolsonaro, the picture was markedly different. Gerp was clearly within the margin, putting him at 46%, just 1.03 points below the final result, with a stated margin of ±2 points. Quaest and Futura were effectively on the boundary: Quaest had him at 45%, 2.03 points below the result with a ±2-point margin, while Futura showed 44.8%, 2.23 points below with a ±2.2-point margin.
Because published polling figures are rounded, differences of just a few hundredths of a percentage point should not be treated as statistically meaningful breaches of the margin.
In the other seven surveys, however, the gap between Flávio Bolsonaro’s polling number and his final result was clearly larger than the stated margin of error. PoderData had him at 43%, 4.03 points below the result, with a ±1.5-point margin. AtlasIntel showed 44.1%, 2.93 points below, with a ±1-point margin. Datafolha had 42%, a 5.03-point gap, with a ±2-point margin.
Real Time Big Data showed 41%, 6.03 points below the final result, also with a ±2-point margin. CNT/MDA had Bolsonaro at 42.1%, 4.93 points below the result, with a ±2.2-point margin.
The largest gaps came from Nexus — commissioned by BTG itself — and Meio/Ideia. After BTG recalculated their figures into valid-vote shares, the surveys put Flávio Bolsonaro at 39.4% and 39.6%, respectively, 7.63 and 7.43 points below his final result.
There is an important methodological caveat in those two cases: BTG converted the published figures into valid-vote shares, while the stated margins of error referred to the original survey results.
That does not mean, however, that eight polls showed Lula with a statistically significant lead. In several surveys, the gap between the two candidates was within the margin of error and was reported as a statistical tie.
The more relevant takeaway, therefore, is not simply that polls had the wrong candidate numerically ahead. It is that virtually every poll captured a smaller share of support for Flávio Bolsonaro than ultimately appeared at the ballot box.
Using the sum of the absolute errors for Lula and Flávio Bolsonaro, Gerp came closest to the final result, with a combined deviation of 2.19 points. Its final survey had Flávio at 46% and Lula at 44%, with both results inside its ±2-point margin of error. Quaest followed with a combined error of 2.87 points.
Still, a poll’s margin of error should not be treated as a simple pass-or-fail test. It mainly captures sampling uncertainty and does not necessarily account for factors such as late shifts in voter preferences, differences in turnout, weighting models, difficulty reaching certain groups or effects related to the polling method itself.
Timing also matters. The surveys were conducted on different dates, and a genuine shift in voter preferences between the end of fieldwork and election day will later show up as a gap between the poll and the final vote — even though that gap is not necessarily a sampling error.
The broader pattern, however, is clear: the polling miss in Brazil’s first round was concentrated far more heavily on Flávio Bolsonaro than on Lula.
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